1. Field of the Invention
The present invention relates to ink cartridges, print heads and ink-jet printers, and more particularly to an ink cartridge attachable to and detachable from a print head of an ink-jet printer, and to a print head and an ink-jet printer using such an ink cartridge.
2. Description of the Prior Art
When the ink runs out, an ink-jet printer becomes instantly incapable of printing; that is, so-called missing dots occur. Accordingly, it is necessary to detect a residual quantity of the ink, to halt the printing operation of the ink-jet printer before the missing dots occur, and to generate an alarm urging a user to supplement the ink. One approach to detect the residual quantity of the ink is a method whereby a pair of electrodes are provided inside an ink tank which stores the ink, and a variation in the value of resistance is monitored by applying a pulse voltage while ensuring that no electrolysis takes place between the electrodes.
Supplement of the ink is a laborious operation. From the viewpoint of the running cost of the ink-jet printer, it is preferable that an ink cartridge which stores the ink be exchanged when the alarm is generated. Various constructions of the ink cartridge are proposed.
FIG. 1 shows an example of conventional ink cartridge in a lateral sectional view and a print head in a side view. Referring to FIG. 1, a print head 501 has an ink needle 503. An ink cartridge 502 has an elastic member 504, an ink 505 and a sponge 506 for creating a negative pressure with respect to the ink 505. The ink cartridge 502 is fitted to the print head 501 such that the elastic member 504 is pierced by the ink needle 503 of the print head 501. In an action reverse to the piercing action, the cartridge 502 is detached from the print head 501.
In normal use, the ink cartridge 502 is detached only when the ink has run out and the ink cartridge 502 is exchanged for a new one. However, the user may need to exchange the ink cartridge 502 in order to use an ink having a different color. Or the user may wrongly recognize that the ink has run out, that is, the ink is depleted, and detach the ink cartridge 502. Or the user may detach the ink cartridge 502 in order to perform a maintenance activity including a cleaning of the print head 501 of the ink-jet printer.
When the ink cartridge 502 is detached from the print head 501 in a state where the ink in the ink cartridge 502 has not run out, the detached ink cartridge 502 is attached again to the print head 501 for continued use. Detaching of the ink cartridge 502 from the print head 501 and re-attaching the same to the print head 501 means that a passage of the ink between the print head 501 and the ink cartridge 502 is cut for a time and then re-established. For this reason, it is inevitable that air bubbles intrude into the print head 501 and the ink cartridge 502 through the passage of the ink, when the ink needle 503 pierces the elastic member 504 again. If left uncontrolled, the air bubbles that intrude into the ink cartridge 502 intrude into the print head 501 sooner or later.
When the air bubbles intrude into the print head 501, missing dots occur at some point of time. Conventionally, a mechanism called a backup unit for protecting the print head 501 is provided. In order to prevent the missing dots, the backup unit is used to remove the air bubbles from a nozzle of the print head 501 by suction. Some ink may also be removed together with the air bubbles unnecessarily when the air bubbles are removed from the nozzle. Hence, there is a problem in that activating the backup unit every time the ink cartridge 502 is attached does not have much advantage because it causes the ink to be wasted.
Further, the air bubbles that intrude into the ink cartridge 502 may come into contact with the electrodes for detecting the residual quantity of the ink, thus causing the value of resistance to vary. Consequently, there is a problem that, despite the fact that a new ink cartridge is attached to the print head 501, the ink is wrongly detected as having run out.
Besides, it is desired that some measure be taken to prevent a leakage of the ink from occurring when the ink cartridge 502 is removed from the print head 501.